This invention relates to an improvement in a damper apparatus in a clutch for a torque convertor used chiefly for a transmission for a vehicle.
The applicant has previously proposed a damper apparatus in a clutch for a torque convertor. A turbine blade wheel connected to an output shaft is positioned in the internal space of a main body of a torque convertor surrounded by an input casing on one side connected to an input shaft and a pump blade wheel on the other side connected to the input casing. A clutch plate is interposed between the turbine blade wheel and the input casing. The clutch plate is arranged to be axially movable to be either engaged with or disengaged from the input casing according to a difference between fluid pressures acting on both side survaces thereof. The clutch plate and the turbine blade wheel are interconnected through a damper spring means to be relatively turnable. The clutch plate is provided with a communication hole for communicating between both side surfaces thereof and with an opening and closing member for opening and closing the communication hole, so that an opening area of the communcation hole may be adjusted by the opening and closing member in accordance with a relative turning displacement amount between the clutch plate and the turbine blade wheel. When the driving force is small and the amount of relative turning displacement is also small, the opening area of the communication hole is increased. The amount of leakage of the fluid through the communcation hole is increased, resulting in decreasing the pressure difference between the opposite side surfaces of the clutch plate. Thus, the engaging force of the clutch plate is weakened in accordance with a decrease in a driving torque. The clutch plate easily slips, and a torque change is absorbed by such slipping.
This apparatus, however, has the problem that even if the opening area of the communcation hole remains unchanged, the amount of leakage of the fluid varies with change of viscosity of the fluid caused by change of temperature. Accordingly, the difference in the pressures of the fluids between the both side surfaces of the clutch plate varies with a change in temperature. Consequently, the engaging force of the clutch plate at the time of a low temperature and at the time of a high temperature differs.